Sorry for the late reply. Some how missed this one.
1 - To do this type of email collection with Zimbra you'll need to configure fetchmail. Marc put a good how-to for that here:
[SOLVED] Fetchmail from other servers (aka account aggregation)
You'd then need to look at our filter options and see which will sort your mail best. Maybe to/from maybe it's some header.
2 - We support multiple account and alias's. How do you plan to use Zimbra? Web interface or via Outlook with IMAP? If you choose the later you can set up a seperate account for each and configure Outlook to send the right FROM address. Currently the web UI does not let you reply with an alias.
3 - With Outlook or Thunderbird yes, but not with the Web UI.
4 - Currently you can't Edit a Feed. If it changes you'll need to create a new folder and move any messages you'd like to keep from the previous. This is pretty simple with drag n drop.
Thanks for the detailed feedback. Not sure if all your questions were regarding our web UI or if you plan to continue to use Outlook as your client. So if something is not clear or you have additional questions please let us know.